Abstract

We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo{sub 4}O{sub 7}.We show that the presence of less than 1% Zn at the Co sites decreases T{sub C} from 64 K to 48 K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54 K and 77 K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50 K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties.

@article{osti_22399164,
title = {Closely related magnetic and dielectric transitions in the “114” magnetoelectric Zn-doped CaBaCo{sub 4}O{sub 7}},
author = {Seikh, Md. Motin and Caignaert, V., E-mail: vincent.caignaert@ensicaen.fr and Preethi Meher, K. R. S. and Maignan, A. and Raveau, B. and Suard, E.},
abstractNote = {We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo{sub 4}O{sub 7}.We show that the presence of less than 1% Zn at the Co sites decreases T{sub C} from 64 K to 48 K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54 K and 77 K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50 K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties.},
doi = {10.1063/1.4905033},
journal = {Journal of Applied Physics},
number = 24,
volume = 116,
place = {United States},
year = 2014,
month =
}

The structural, elastic, magnetic, and magnetoelectric properties of the CaBaCo{sub 4}O{sub 7} multiferroic are experimentally studied and compared with the properties of the related YBaCo{sub 4}O{sub 7} cobaltite, where Y{sup 3+} ions substitute for Ca{sup 2+} ions. Unlike the frustrated YBaCo{sub 4}O{sub 7} magnet, the softening of Young’s modulus and the hysteresis in the ΔE(T)/E{sub 0} curve of ferrimagnetic CaBaCo{sub 4}O{sub 7} in the paramagnetic region are weak, and the anomaly during the magnetic transition increases by almost an order of magnitude. This difference can point to different characters of the development of a long-range magnetic order in these twomore » cobaltites. The distortion of the crystal structure that removes the frustrations of exchange interactions is found to correlate with the magnetic behavior of the cobaltites under study. The magnetization curves of the Ca cobaltite have two steps below 15 K, which can point to the presence of a metastable state in a high magnetic field. The study of the longitudinal and transverse magnetoelectric effects in a pulsed magnetic field demonstrates that their magnitudes are maximal near T{sub C} and change their character from linear to quadratic during passage through this temperature.« less

A three-phase BaTiO{sub 3}-CoFe{sub 2}O{sub 4}-poly(vinylidene-fluoride) (BT-CF-PVDF) particulate composite showing a maximum magnetoelectric voltage coefficient alpha{sub E33}approx26 mV/cm Oe, at a small applied magnetic field H{sub DC}=263 Oe, has been demonstrated in this work. Large magnetoelectric response in this composite (particulate BT-CF embedded in PVDF matrix) is possibly a result of the effective mechanical interaction between CF and BT through the PVDF matrix. Processing temperatures for composite preparation are low, ensuring no chemical reaction or interdiffusion between the atoms of piezoelectric and magnetostrictive phases, leading to large value of magnetoelectric voltage coefficient. Detailed measurements of dielectric, magnetic, and static magnetoelectricmore » data are reported. Peak in the dielectric spectrum is shown to correlate with the buildup of magnetization in the composite. Although the M-H loop gives M{sub s}, M{sub r}, and H{sub c} (=37.2 emu/g, 16.4 emu/g, and 830 Oe, respectively) in accordance with the expected values (wt % of CF in the composite is 52.5%), the overall magnetic behavior of the composite is identified as 'spin glass'.« less

In this paper, the magnetoelectric coupling and ferroelectric ordering of the orthorhombic Dy{sub 1-x}Ho{sub x}MnO{sub 3} (x = 0 and 0.1) are studied from the magnetodielectric response of the polycrystalline samples. The dielectric study on the DyMnO{sub 3} reveals ferroelectric transition at 18 K along with an addition transition at 12 K. We suggest that the transition at 12 K could have originated from the polarization flop rather than being the rare earth magnetic ordering. The magnetodielectric study reveals a magnetoelectric coupling strength of 10%, which is stronger by two orders of magnitude in comparison to the hexagonal manganites. Surprisingly, the Ho{sup 3+} substitution inmore » DyMnO{sub 3} suppresses the magnetoelectric coupling strength via the suppression of the spiral magnetic ordering. In addition, it also reduces the antiferromagnetic ordering and ferroelectric ordering temperatures. Overall, the studies show that the rare earth plays an important role in the magnetoelectric coupling strength through the modulation of spiral magnetic structure.« less

We investigate the magnetoelectric effect in Sr{sub 2}CoGe{sub 2}O{sub 7}, which has a two-dimensional magnetic interaction between Co ions in the ab plane. This compound shows a weak magnetism and field-induced magnetic transition below the temperature of 7 K. It does not exhibit electric polarization under zero magnetic field. However, by applying an external magnetic field, the electric polarization is induced around its Néel temperature and increases with increasing magnetic field. The induced electric polarization in Sr{sub 2}CoGe{sub 2}O{sub 7} is almost two orders of magnitude smaller than that of Ba{sub 2}CoGe{sub 2}O{sub 7}. This result suggests that the different ionicmore » radius of the strontium and the barium anion plays a key role in determining the property of electric polarization. The origins of electric polarization and magnetoelectric effect are discussed.« less